In a skillet over medium heat, brown the lean ground beef until fully cooked. Make sure to drain any excess fat.

Using the same skillet, sauté the chopped onion and minced garlic until they become translucent, about five minutes.

Transfer the browned beef and sautéed onions and garlic to the slow cooker. Add the diced tomatoes, kidney beans, black beans, chili powder, cumin, salt, and pepper. Stir well to combine.

Cover the slow cooker and set it to cook on low for 6 hours or high for 3 hours.

Before serving, taste your Slow Cooker Chili and adjust the seasoning if needed.